Sail furling devices are widely employed on sailing vessels to enable complete or partial furling and unfurling of a foresail, in which the sail is rolled up around its leading edge or luff and around a stay. Many of these devices include an elongate rigid foil having an internal channel rotatably mounted around the stay and an external channel for receiving and supporting the luff of the sail.
Conventional furling gear usually includes an upper swivel arrangement connected to the upper end of the foil and a lower rotary drive means connected to the bottom of the foil, such as a line wrapped on a drive or an electric or hydraulic motor. The foil is rotated by the drive means to roll up and furl the sail. The foil can also rotate in the reverse direction, and unfurling is accomplished by pulling on the normal trimming sheet attached to the clew of the sail.
Various forms of foils for supporting a jib are known, as shown in U.S. Pat. Nos. 3,802,373, 4,619,216 and Re. 31,829. Such foils may include more than one sail receiving groove to allow a change of sails while the original sail remains hoisted. A furling foil comprising a one-piece structure of inner and outer extruded metal tubes is shown in U.S. Pat. No. 4,637,334.
Since a furling foil is very long in comparison with the cross-sectional dimensions, the amount of resistance to torsion during furling is a critical concern. Any excessive twisting of the foil around its longitudinal axis may cause uneven rolling up of the sail, resulting in distortions in the sail, or even permanent damage to the foil itself.
In order to obtain a high degree of torsional resistance in a furling foil, it is known to fabricate the foil from high strength rigid materials, such as extruded aluminum. Unfortunately, however, such foils in their finished elongated form are nonresilient along their length and are easily damaged or permanently bent out of shape if lateral bending forces are applied. As a consequence, such foils must be produced and shipped in short sections and cannot be produced, coiled and shipped in a single continuous piece. The foil sections must be later permanently secured together around the stay by the consumer or a professional fitter during installation of the furling gear, with the mast raised. The finished foil is easily damaged when struck by other objects, such as a spinnaker pole. Also, if the mast is lowered at a later time, such as when a sailboat is stored or placed on a trailer for transport, precautions must be taken to avoid permanent damage to the fragile foil. Removal and storage are especially troublesome since the foil must be removed from its protective position around the stay, and the foil is longer than the mast. Also, the foil tends to be weaker at the area of the joints.
While it would be highly desirable to provide a one-piece furling foil having high torsion resistance but still capable of being bent or coiled along its length in a recoverable fashion, no acceptable solution has been forthcoming. It is known from U.S. Pat. No. 4,821,664 to provide a furling foil composed entirely of a thermoplastic polymer, such as polyvinyl chloride. Such foils can be constructed in a diameter which allows some degree of lengthwise flexibility. A serious drawback is that such foils have low torsional resistance, and twists of more than one complete turn are specified for a normal furling operation. This may cause distortion of the sail in a partial furling operation. A second drawback is that these plastic foils can become permanently distorted or set in a twisted state in sunlight and heat.
Another proposal is found in U.S. Pat. No. 3,872,816. The foil comprises a chain formed of interlocking links to resist torsional forces imposed by the furling winding drum. In practice, however, such chains are bulky and heavy, and no provision can be made for supporting the luff of the sail in an external groove.